The invention relates to a fuel injection system of the type set forth in the appended claim 1. A fuel injection system provided with a conditioning member that transversely penetrates the air intake manifold has been known, particularly the type wherein the conditioning member, during its opening movement following the operation of the throttle element, is moved in opposition to a resetting force and, in the full-load position of the throttle element, is adapted to maintain a certain minimum pressure drop, i.e., it serves for a better conditioning of the fuel-air mixture in the full-load range. However, this fuel injection system does not permit the conditioning of the injected fuel with air directly after injection, so that there is the danger that fuel will be precipitated onto the manifold walls.